A network of rapidly filling and emptying lakes lies beneath at least two of West Antarctica's ice streams, new research suggests.
The findings will be published online by the journal Science, at the Science Express website, on Thursday, 15 February. Science is the journal of AAAS, the nonprofit science society.
More than 100 subglacial lakes have already been discovered, but the new ones are particularly interesting because they occur below fast-moving ice. Though it's too early to say exactly how this liquid water is affecting the rates of ice flow above, understanding the behavior of these fast-moving ice streams is essential for predicting how Antarctica may contribute to sea level rise.
Helen Fricker of the University of California San Diego's Scripps Institution of Oceanography and colleagues analyzed elevation data recorded by NASA's Ice Cloud and land Elevation Satellite (ICESat) collected over the lower parts of the Whillans and Mercer Ice Streams. These are two of the major, fast-moving glaciers that are carrying ice from the interior of the West Antarctic Ice Sheet to the floating Ross Ice Shelf.
"We've found that there are substantial subglacial lakes under ice that's moving a couple of meters per day. It's really ripping along. It's the fast-moving ice that determines how the ice sheet responds to climate change on a short timescale," said Robert Bindschadler of NASA Goddard Space Flight Center, one of the study's coauthors.
"We aren't yet able to predict what these ice streams are going to do. We're still learning about the controlling processes. Water is critical, because it's essentially the grease on the wheel. But we don't know the details yet," he said.
Glaciologists have known that water exists under ice streams, but the observation of a system of water storage reservoirs is unprecedented. The surprising thing about this discovery is the amount of water involved, and the pace at which it moves from one reservoir to another, according to lead author Helen Fricker.
"We didn't realize that the water under these ice streams was moving in such large quantities, and on such short time scales," Fricker said. "We thought these changes took place over years and decades, but we are seeing large changes over months."
The authors identified numerous spots that either rose or deflated from 2003 to 2006, likely because water flowed into or out of them. Water would be capable of this because it is highly pressurized under the weight of the overlying ice.
The three largest regions are between approximately 120 and 500 square kilometers, while the others are widely scattered and smaller. One of the large regions, referred to as Subglacial Lake Engelhardt, drained during the first 2.7 years of the ICESat mission, while another, Subglacial Lake Conway, steadily filled during the same period.
"I'm quite astonished that with this combination of satellite sensors we could sense the movement of large amounts of water like this. From 600 kilometers up in space, we were able to see small portions of the ice sheet rise and sink," Bindschadler said.
Studies of the subglacial environment are rare, being expensive, risky and labor-intensive. Bindschadler explained that before the ICESat mission, researchers would typically have to drill holes in the ice streams in order to study what was occurring beneath them. These holes, generally just about 4 inches in diameter, provided a much more limited view of the entire ice stream than the satellite images do.
"Until now, we've had just a few glimpses into what's going on down there. This is the most complete picture to date what's going on beneath fast flowing ice," Bindschadler said.
Fricker added, "The approach used for this work provides glaciologists with a new tool to survey and monitor the nature of the subglacial water system and to link these observations to the motion of the ice sheet. We still don't know how the subglacial water system varies on longer time-scales from decades to centuries. To do this, we need to continue monitoring the ice streams with ICESat and future follow-on missions."
"An Active Subglacial Water System in West Antarctica Mapped From Space," by Helen Amanda Fricker at Scripps Institution of Oceanography in La Jolla, CA and University of California, San Diego in La Jolla, CA; Ted Scambos at University of Colorado in Boulder, CO; Robert Bindschadler at NASA Goddard Space Flight Center in Greenbelt, MD; Laurie Padman at Earth & Space Research in Corvallis, OR. This research was supported by NASA.
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